The actress had a ten-year stint in Weatherfield until 1971, when Valerie was killed by an electric shock while using a hairdryer.
Speaking in an interview with the Radio Times, Reid explained that she was eager to try comedy when she brought her time on the cobbles to an end.
She commented: "Darling, I was a basket case when I left! I'd already had too much of it. That kind of work suits some people, but it didn't suit me.
"It was my decision to leave and I was desperate, really desperate, to go. Because I knew I was good at comedy and there was no way that Valerie Barlow was ever going to be funny."
Reid recently appeared in the BBC's three-part Upstairs, Downstairs revival and will soon be seen in ITV1's Marchlands, which begins on February 3.